Two undergrad students at Duke University’s Pratt School of Engineering have designed a device that is essentially like a solar panel array; it would "harvest" power from alternative sources such as a WiFi signal in order to recharge an electronic device; this could potentially render the plug in charger obsolete.

The device wirelessly converts the microwave signal to direct current voltage capable of recharging a cell phone battery or other small electronic device, according to a report appearing in the journal Applied Physics Letters in December 2013. (It is now available online.)

It operates on a similar principle to solar panels, which convert light energy into electrical current. But this versatile energy harvester could be tuned to harvest the signal from other energy sources, including satellite signals, sound signals or Wi-Fi signals, the researchers say.

The key to the power harvester lies in its application of metamaterials, engineered structures that can capture various forms of wave energy and tune them for useful applications.

Undergraduate engineering student Allen Hawkes, working with graduate student Alexander Katko and lead investigator Steven Cummer, professor of electrical and computer engineering, designed an electrical circuit capable of harvesting microwaves.

They used a series of five fiberglass and copper energy conductors wired together on a circuit board to convert microwaves into 7.3V of electricity. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V.

“We were aiming for the highest energy efficiency we could achieve,” said Hawkes. “We had been getting energy efficiency around 6 to 10 percent, but with this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells.”

“It’s possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting,” Katko said. “Until now, a lot of work with metamaterials has been theoretical. We are showing that with a little work, these materials can be useful for consumer applications.”

With additional modifications, the researchers said the power-harvesting metamaterial could potentially be built into a cell phone, allowing the phone to recharge wirelessly while not in use. This feature could, in principle, allow people living in locations without ready access to a conventional power outlet to harvest energy from a nearby cell phone tower instead.

Via Duke University’s Pratt School of Engineering